Look for a 12A408 Thermostat Housing. They did fit them on some Morris Minors and some MG Models. They seem a little thin on the ground in the UK ?? but quite readily available in these parts;-
https://minisport.co...th-temp-adaptor
These take the stock Mini Temp sender.
Thread bump... Do you know if the Morris Minor equivalent used a different thread? Seen some posts online which state 3/8 BSP?
The only covers I have come across has a 5/8" UNF Thread with the tapered seat, just like that in the Heads.
I'm pretty sure I have one in the box, if I remember, I'll snap off some photos.
If I recall, Kilkenny Castings make them here;-
https://www.kcautopr...ingsmorris.html
WO16S